1. Field of the Invention
The invention relates to a drive for machine components such as carriages, gripping devices or the like, comprising at least one threaded spindle which can be driven by at least one motor and on which nuts are positioned, wherein at least one of the nuts is connected with the machine component and wherein the nuts are in engagement with spindle sections having oppositely oriented axial pitch.
2. Description of the Related Art
Because of the required precision, the axle movements of machine tools as well as simple and combined linear and rotational movements of workpieces and tools must follow very exactly, essentially without delay, and with a high degree of repeating accuracy the preset values of the numerical control, and this is to be achieved independent of the acting counter forces such as feed force, friction, or acceleration forces of the linearly or rotationally driven masses. The moving speed and the acceleration must be as high as possible in order to take up as little time as possible for a precise positioning.
In known drive systems a rotary current synchronous motor mounted on the machine frame drives a ball screw spindle rotatably supported on the machine frame. The spindle engages a nut which is fixedly connected in a carriage or a stand. The carriage or the stand are longitudinally movable on guides relative to the machine frame. As a function of the stroke length or the required rapid traverse of the carriage, the spindle and the nut have different limits of rotational speed. Above certain slenderness ratios, or for other constructive reasons, the ball screw spindle can also be positioned so as to be fixed in regard to rotation and the nut can be driven in rotation instead.
Moreover, drives are known from European patent application 1 013 373 A1 which provide a second drive motor for driving the threaded spindle or the nut for the purpose of increasing the moving speeds and accelerations.
Furthermore, spindle drive devices are known from German patent application 39 38 353 which, by means of two spindle drive heads and one spindle with right-hand and left-hand thread on the same threaded spindle section, perform translatory as well as rotary movements.
Also, threaded spindles are known which have left-hand and right-hand threads on two adjacent spindle sections and are used for a central clamping of workpieces (Heinrich Matuszewski, Handbuch Vorrichtungen: Konstruktion und Einsatz, Verlag Vieweg, 1986, page 123).
The technical limits of these known drive systems lie in the rotational speed rating of the ball screw spindles and in the rotational speed rating of commercial servo motors. The doubling of the moving speed requires for the same axial spindle pitch a doubling of the motor speed. When the motor speed increases past the speed of maximum torque, the motor torque decreases as a matter of the functional limitations of the motor, and this causes the acceleration to decrease. Also, when doubling the motor speed, the run-up time of the motor increases. An increase of the axial pitch is possible; however; this requires that the spindle diameter must be increased which would result in higher mass moments of inertia.
It is an object of the present invention to configure the drive of the aforementioned kind such that for high positioning speeds in the case of handling devices and high-speed cutting with machine tools the acceleration as well as the rapid traverse speeds and feed speeds are high.
In accordance with the present invention, this is achieved in that one of the two nuts is spatially fixed and that the drive moment is introduced via the threaded spindle.
With the drive according to the invention, the drive moment is introduced by means of the threaded spindle. By using a threaded spindle with two spindle sections having oppositely oriented pitch and a nut which is spatially fixed, an increase of the acceleration and of the moving speeds of the machine component is achieved for the same motor speed.